BackgroundThe 1996 Safe Drinking Water Act (SDWA) amendments require that once every five years EPA issue a new list of no more than 30 unregulated contaminants to be monitored by public water systems (PWSs). The first Unregulated Contaminant Monitoring Rule (UCMR 1) was published on September 17, 1999 and the second (UCMR 2) was published on January 4, 2007. This monitoring provides a basis for future regulatory actions to protect public health.

About this ruleUCMR 2 required public water systems (PWSs) to monitor for 25 chemical contaminants under two lists:

Assessment Monitoring (List 1 contaminants) uses common analytical method technologies used by drinking water laboratories. For UCMR 2, all PWSs serving more than 10,000 people and 800 representative PWSs serving 10,000 or fewer people were required to monitor for the 10 List 1 contaminants during a 12-month period from January 2008 through December 2010.

Screening Survey (List 2 contaminants) monitoring uses specialized analytical method technologies not as commonly used by drinking water laboratories. All PWSs serving more than 100,000 people, 320 representative PWSs serving 10,001 to100,000 people and 480 representative PWSs serving 10,000 or fewer people are required to monitor for 15 List 2 contaminants during a 12-month period from January 2008 through December 2010.

EPA paid for the analysis of all samples from systems serving 10,000 or fewer people.

Why was the UCMR program developed?The UCMR program was developed in coordination with the Contaminant Candidate List (CCL). The CCL is a list of contaminants that are not regulated by the National Primary Drinking Water Regulations, are known or anticipated to occur at public water systems and may warrant regulation under the Safe Drinking Water Act. Data collected through UCMR are stored in the National Contaminant Occurrence Database (NCOD) to support analysis and review of contaminant occurrence, to guide the CCL selection process, and to support the Administrator's determination of whether to regulate a contaminant in the interest of protecting public health.

How did EPA select these contaminants?EPA reviewed contaminants that had been targeted through existing prioritization processes, including previous UCMR contaminants and the Contaminant Candidate List (CCL). Additional contaminants were identified based on current research on occurrence and health effect risk factors. Pesticides that were not registered for use in the United States, contaminants that did not have an analytical reference standard and contaminants whose analytical methods were not ready for use were removed from the list. EPA further prioritized the remaining contaminants based on more extensive health effects evaluations by the Office of Water’s Office of Science and Technology. These procedures for evaluating health effects were developed to support the ranking of contaminants for future CCLs.

What are the environmental and public health benefits of UCMR?UCMR benefits the environment and public health by providing EPA and other interested parties with scientifically valid data on the occurrence of these contaminants in drinking water, permitting assessment of the population being exposed and the levels of exposure. This data set is one of the primary sources of occurrence and exposure information the Agency uses to develop regulatory decisions for emerging contaminants.